The rejuvenation and reclamation of used active carbon by heating the electrically conductive used active carbon by applying an electric current is disclosed in the prior art. One of these prior art processes employs an electric current directly applied to a quantity of particulate used active carbon accumulated between two vertical electrode plates arranged face-to-face (Accumulation Method). Another method treats the used active carbon by filling a space between two face-to-face vertical electrode plates with downwardly moving particles of the used active carbon and simultaneously applying an electric current to the particles (Moving Layer Method). Still another prior art method is similar to the "Moving Layer Method" but provides additional vertical electrodes arranged in a horizontal plane through which the particles flow (Method Using Plurality of Vertical Electrodes In A Horizontal Plane).
The Accumulation Method has the drawback that only a batch type operation is possible, so that this method is unsuitable for a continuous reclamation of the used active carbon. Another drawback of the accumulation method is that the desorption of the materials adsorbed on the active carbon requires a complicated procedure in which the applied voltage must be controlled in the course of desorption, because the electrical resistance of the individual particles accumulated between the electrodes changes gradually in the course of desorption as the contaminants are desorbed. This Accumulation Method is further limited by the difficulty of establishing a voltage control system capable of coping with the fluctuations in the amount of materials adsorbed on the used active carbon (adsorbed carbon) and in the amount of carbon filling the space between the electrodes.
On the other hand, while the Moving Layer Method is suitable for continuous reclamation of the used active carbon, it has the drawback that the electric current is applied at a right angle to the particle flow and therefore is not uniformly applied to the particles flowing between the electrode plates. This is due to the fact that the electrical resistance of the carbon particles undergoes a change in the course of desorption. Specifically, the apparent electric resistance of the particles in the moving layer of the active carbon containing adsorbed contaminants has a higher value than that of like carbon particles having no adsorbed contaminants and higher than that of the reclaimed active carbon. Therefore, the electrical resistance distribution in the layer formed with the particles of adsorbed carbon between the two vertical electrode plates arranged face-to-face in the column has a higher value near the upper end of the electrode plate than at the lower end. When voltage is applied to the electrode plates, therefore, the current is biased toward the lower end of the electrode plate and therefore is concentrated there. As a result, the heat generation of the particles of adsorbed carbon takes place only near the lower end of the electrode plate. According to this method, the heat generation in the part of the particle-moving layer formed with the particles of adsorbed carbon causes heat transfer to take place in an upper particle-layer adjacent to the lower ends, but the whole of the particle-moving layer constitutes a downward-flowing layer, so that the heat transfer is only produced within a narrow range. Therefore, to obtain a uniform desorption of materials adsorbed on the carbon particles, the length of the electrode plates must be considerably increased to compensate for the inefficient heat transfer. Therefore, the apparatus size must be increased and for this reason, the moving layer method has been criticized as being impractical.
The method for heating used active carbon by providing a plurality of additional vertical electrodes arranged in a horizontal plane of the particle-flowing passage and then applying an electric current to the particles passing between these electrodes, is often effective, when an experimental device small enough to uniformly heat the whole sectional area is used, because the particle-flowing passage has a comparatively narrow sectional area. As previously explained, however, this method has also the defect that the flow of an electric current becomes non-uniform and unstable, as in the case of the particles flowing down between opposing electrode plates.